1. Field of the Invention
This invention relates to synthetic polymers, and more particularly concerns a water-swellable polyamide in a water-permeable physical form and useful for the absorption of ions from aqueous systems.
2. Description of the Prior Art
A chelating polymer produced by the interaction of polyethyleneimine (PEI) with nitrilotriacetic acid (NTA) is disclosed in U.S. Pat. No. 3,715,339. By utilizing a high ratio of NTA and PEI, the chelating polymer has a preponderance of pendant carboxyl groups which afford high affinity for multi-valent cations. Such polymers absorb water in the amount of between 100 and 600 percent of the dry weight of the resin to achieve a gel-like consistency. Accordingly, a bed of granules of such polymer presents a very high resistance to the flow of liquid therethrough.
U.S. patent application Ser. No. 395,535, filed 08/18/89 now U.S. Pat. No. 5,002,984 discloses a product wherein the wall structure of a porous cellulosic sponge supports a polymer such as those of U.S. Pat. No. 3,715,339 wherein the ratio of NTA/PEI which produces the polymer is preferably between 1.00 and 1.45. By virtue of its disposition upon a porous sponge, the polymer-containing product can be employed in fish net confining means in rivers, and is substantially unaffected by water-borne suspended matter.
U.S. Pat. No. 4,332,916 discloses the chemical binding of PEI to a cellulose sponge by use of a special sulfonium chloride crosslinking agent. However, the amount of chemically bound PEI, determined by calculation from Example 3 therein, is at most 5.5%. At such small level of PEI, the sponge is not capable of absorbing significant amounts of ions, and presumably finds use primarily in monitoring water quality.
In various metal mining operations, conditions are often encountered, especially after abandonment of the mine, where streams of acidic metal-laden water emerge from the former mine area. Such acid mine drainage water may typically have a pH in the range of 2.5-6.5 and may contain toxic transition metal ions such as cadmium, cobalt, nickel and lead. Although the sponge-supported polymer of said Patent Application absorbs said toxic ions, it also absorbs highly abundant innocuous multivalent ions such as aluminum, calcium and magnesium. By absorbing such abundant ions, its capacity for absorbing the toxic transition metal ions is severely diminished.
It is accordingly an object of the present invention to provide a polymer capable of absorbing transition metal ions while having little affinity for multi-valent non-transition metal ions such as aluminum, calcium and magnesium.
It is another object of this invention to provide a polymer as in the foregoing object in a physical form presenting little impedance to the flow of water in contact with said polymer.
It is a further object of the present invention to provide a polymer of the aforesaid nature disposed upon a porous sponge and capable of absorbing significant amounts of transition metal ions while being substantially unaffected by water-borne suspended matter.
These objects and other objects and advantages of the invention will be apparent from the following description.